1. Field of the Invention
Forming layered ohmic contacts to n type GaAs.
2. Prior Art
Alloyed ohmic contacts to GaAs have been known and used for many years. It has not been established that alloyed contacts reduce barrier height at GaAs interfaces.
Nonalloyed ohmic contacts to GaAs and other semiconductors are increasingly important as device dimensions decrease. Many semiconductors (including GaAs) exhibit a narrow range of Fermi level positions at the interfaces of electrical contacts. This range is typically not optimum for nonalloyed tunneling ohmic contact applications because the specific contact resistance depends exponentially on barrier height. Gallium Arsenide is a semiconductor where the Schottky barrier height on n type material is usually limited to a narrow range (0.7 to 0.9 eV) for metal contacts. This large barrier is thus an impediment to achieving a low ohmic contact resistance. In one approach to a nonalloyed ohmic contact to GaAs, a 0.5 eV Au Schottky barrier contact is made to a .about.250 .ANG. thick Ge heterojunction layer grown epitaxially onto the GaAs, which has the effect of transferring the primary barrier to current flow from the metal-GaAs interface to the metal-Ge interface (R. Stall, et al, Electron. Lett. 15 800 (1979).